1. Field of the Invention
This invention relates to a method of producing hardened inorganic products, and more particularly to a method of producing hardened inorganic products from hydraulic materials.
2. Prior Art
Slag is known to harden as it undergoes hydration in the presence of an alkaline stimulant (such as calcium hydroxide, sodium hydroxide, potassium hydroxide, etc.). A variety of applications thereof have been contemplated and practiced. By way of illustration, blast furnace cement has been produced by blending Portland cement as an alkaline stimulant with slags. There have been practiced methods of producing hardened inorganic products from hydraulic materials comprising slag as an effective component (hereinafter represented by slag). However, although slag undergoes a hydration reaction to yield an inorganic hardened product, the rate of hardening of slag is so low that the product has only a low initial strength, high density and low impact resistance.
For the purpose of achieving a necessary initial strength or a reduction of weight, there is also known a method of producing a TSH-containing hardened product comprising the the steps of admixing gypsum with a slag system so as to generate ettringite (hereinafter referred to as TSH) on hydration and hardening.
However, in these methods, the hydration reaction is unstable and causes various troubles. Thus, a slag-gypsum system does not exclusively yield TSH but gives a mixture of TSH and calcium aluminate monosulfate hydrate (hereinafter referred to as MSH) which is lean in gypsum component, and while TSH is produced nearly exclusively in a comparatively low temperature region (near atmospheric temperature) and, therefore, the system is advantageous in the sense of producing TSH in the system, the hardened product produced under such conditions was inadequate in terms of physical properties, and it has been impossible to obtain practically useful plates. For example, if aging is performed at a temperature below 50.degree. C., TSH is produced but the plate produce has a poor resistance to freezing, and its strength is about 10 percent lower. While the reasons why such properties are adversely affected remain yet to be made clear, it is suspected that crystals of TSH so produced are so large as to cause multiple voids in the hardened product and that since the conversion to TSH progresses too fast as compared with the hardening of slag, the two components are not sufficiently intertwined. Moreover, it is suspected that as water finds its way into the above-mentioned voids and freezes there, it causes a breakdown of the system and, hence, the so-called freeze hazards.
On the other hand, for the purpose of improving the physical properties of the plate, if aging is performed under hot humid conditions at a temperature in excess of 50.degree. C., there occurs a drastic decrease in yield of TSH with an inversely proportional increase in the amount of MSH. Such a matrix leads to decreases in freeze resistance and other physical properties. In such cases, the production of TSH and MSH and the residue of gypsum can be demonstrated by X-ray diffraction analysis. The X-ray diffraction pattern of the matrix shows that while the hydration reaction causes a large decrease of gypsum, there is no correspondingly large increase of TSH, suggesting the formation of intermediates. One of such intermediates is MSH.
While the above facts suggest that an actual variation of aging temperature results in marked changes in the composition and physical properties and, in fact, such phenomena have been actually observed and have presented problems in the production of hardened inorganic products. By way of illustration, in the production of a building panel or plate, it is actually impossible to avoid a non-uniform distribution of temperature in the aging process, but such a local variation (or scattering) of temperature results in a local non-uniformity of the proportions of TSH and MSH in a single plate, thus causing deterioration in the freeze resistance, strength and other properties of the plate. In some instances, the plate may crack and warp.
In the case of blast furnace cement, the balance between the above-mentioned formation of ettringite and the state of hardening is adversely affected so that workability is affected. Blast furnace cement is a mixture of slag and Portland cement, and the Portland cement undergoes hydration to give lime which, in turn, acts as an alkaline stimulant. Therefore, if aging is conducted in the neighborhood of atmospheric temperature, the physical properties of the plate are adversely affected for the reasons mentioned above. Increasing the aging temperature does not lead to the desired formation of TSH, and the physical properties of the product will not be satisfactory. And the formation of TSH continues even after the product has been shaped into the final form, thus causing an expansion of volume due to the formation of TSH crystals at later dates. As a result, the resistance of the plate to freezing and subsequent degradation is adversely affected. Moreover, in some cases, there occur such faults as the warping, cracking and dimensional change of the plate, deterioration of water resistance, etc. Thus, the product will have such drawbacks as an unsatisfactory service life of the plate in prolonged use.
This invention has been accomplished under the above-mentioned circumstances.